JP2005294417A - Method for manufacturing rare-earth magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a rare-earth magnet wherein a protection layer with less defect can be formed and which can appropriately keep magnetic characteristic. <P>SOLUTION: The method for manufacturing a rare-earth magnet is used to manufacture a rare-earth magnet having a protection layer formed on its surface, and it includes a step wherein an organic monomer-containing liquid is applied to a magnet base body containing rare-earth elements, and an electron beam is irradiated to cause polymerization reaction, so that a high polymer protection layer may be formed on the surface of the magnet base body. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a rare earth magnet, in particular, a rare earth magnet having a protective layer on the surface.

  Rare earth magnets are known as high performance permanent magnets. Rare earth magnets are not only used for household appliances such as conventional air conditioners and refrigerators, but are also being applied to drive motors for industrial machines, robots, fuel cell vehicles, hybrid cars, etc. It is expected that energy saving can be realized. Among such rare earth magnets, R—Fe—B (R is a rare earth element) type magnet is attracting attention because it is a high performance magnet exhibiting a high energy product exceeding 25 MGOe.

  However, such rare earth magnets are extremely susceptible to oxidation because they contain rare earth elements and iron as the main components of the magnet. Moreover, it has a property of low resistance to temperature. Therefore, these magnets tend to have low corrosion resistance, and it has been difficult to avoid deterioration of magnetic characteristics over time due to long-term use.

  Therefore, when such an R—Fe—B rare earth magnet is used, a protective film is formed on the surface of the magnet body for the purpose of improving its corrosion resistance. As a method for forming the protective film, a chemical or physical vapor deposition method or the like is mainly performed.

  On the other hand, as a simpler and more productive method, a method of thermally oxidizing the surface of the magnet body to form an oxide film as a protective layer on the surface of the magnet body has been proposed (for example, Patent Document 1). In this method, since the surface of the magnet body is converted to form the protective layer, there is very little inconvenience when the film is formed on the surface of the body as described above.

  Although the method of patent document 1 is a very simple method, since long-time heat processing of 10 minutes-10 hours is implemented on 200-1100 degreeC high temperature conditions, the magnet element | base_body by such heat processing is carried out. There was a tendency for deterioration to occur. For this reason, the rare-earth magnet obtained in this way has significantly deteriorated in magnetic properties as compared with a magnet body in which no protective layer is formed.

Therefore, as a method for forming a protective layer without high-temperature heating, a technique for forming a polymer thin film on the outermost surface of the rare earth magnet and protecting the surface of the rare earth magnet has been proposed. In this method, a coating material containing a monomer and a polymerization initiator is applied to the surface of the magnet body, and this is heated to 100 to 200 ° C. to cause a polymerization reaction, thereby forming a polymer protective film.
JP 2002-57052 A

  However, in the case of a polymer protective film used at the time of forming a conventional polymerization initiator, pinholes are often formed at the time of polymerization, and it is difficult to realize a function as a surface protective film of a rare earth magnet. It was.

  Therefore, the present invention has been made in view of such circumstances, and provides a method for producing a rare earth magnet capable of forming a protective layer with few defects and maintaining good magnetic properties. Objective.

  In order to achieve the above object, a method for producing a rare earth magnet according to the present invention includes a deposition step of forming an organic material layer containing an organic starting material on a magnet body containing a rare earth element, and a magnet body provided with the organic material layer. And an electron beam irradiation step of irradiating an electron beam.

  In the method for producing a rare earth magnet of the present invention, a polymerization reaction step of forming a protective layer by causing a polymerization reaction in an organic material layer applied to the surface of an element body by irradiating an electron beam in the electron beam irradiation step. It becomes. In such a polymerization reaction step, a polymerization reaction can be caused without adding a polymerization initiator to an organic starting material, for example, a monomer.

  Since the polymerization reaction can be carried out without using a polymerization initiator as in the present invention, defects in the protective film (for example, pinholes, etc.) due to the residual polymerization initiator can be avoided. In addition to those that contribute to radical generation and the like, there are polymerization initiators that remain unreacted. Such residual polymerization initiators tend to generate radicals by receiving external energy (heat, light, etc.) to induce an oxidation reaction in the polymer. This may cause the matrix in the polymer to dissociate and cause defects in the polymer film.

  Whether or not a cross-linking reaction occurs in the organic layer by electron beam irradiation depends on the nature of radicals generated by electron beam irradiation. That is, organic materials are broadly classified into a crosslinking type in which a crosslinking reaction is promoted by electron beam irradiation and a decomposition type in which a decomposition reaction is promoted. In the case of the crosslinking type, radicals are generated by electron beam irradiation, and these are bonded to each other, whereby the polymerization reaction is promoted and the molecular weight tends to increase. In the case of the decomposition type, the main chain tends to be cleaved along with radical generation, and the molecular weight tends to decrease.

  The organic starting material of the present invention refers to a material that is a raw material for the polymer that forms the protective layer. Specifically, it is preferable to use a cross-linking monomer. As the crosslinking monomer, ethylene, propylene, styrene, vinyl chloride, vinyl fluoride, vinylidene fluoride, acrylic acid ester, butadiene, chloroprene, siloxane, ester, amide, imide, and the like can be used. By using at least one of these monomers, a cross-linking reaction by an electron beam can be caused, and the polymer film surface does not become hydrophilic, so that durability against an environment such as external humidity can be enhanced. These monomers may be used as a mixture of plural kinds.

  Moreover, you may use the oligomer which has a radically polymerizable unsaturated group for the organic starting material of this invention. As such an oligomer, for example, unsaturated polyester, unsaturated acrylic, epoxy acrylate, urethane acrylate, polyester acrylate, polyether acrylate, polyene / polythiol, and the like can be used. By using at least one of these oligomers, a cross-linking reaction by an electron beam can be caused, and the polymer film surface does not become hydrophilic, so that durability against an environment such as external humidity can be enhanced. Further, the oligomer may be used by mixing with one or more of the above-mentioned crosslinking monomers. A plurality of oligomers may be mixed and used.

  In the deposition step of the present invention, the organic starting material is preferably evaporated on the surface of the magnet by evaporating in a vacuum using a thin film forming method, for example, an evaporation method. Alternatively, the monomer or oligomer can be applied directly to the magnet surface. Or it can disperse | distribute and apply | coat to a suitable solvent. By using these methods, an organic layer can be formed on the surface of the rare earth magnet with a uniform film thickness.

  The electron beam irradiation process of the present invention is preferably performed in an inert gas atmosphere or in a vacuum. Since electron beams generally have a very high dose rate, it may be possible to prevent an oxidation reaction from occurring in a polymer film being formed during electron beam irradiation. However, in many monomers / oligomers, the polymerization reaction tends to be inhibited by the reaction between radicals generated by electron beam irradiation and oxygen. By performing the electron beam irradiation in an inert gas atmosphere or in a vacuum, the polymerization reaction of various monomers / oligomers can be carried out rapidly.

  The rare earth element preferably contains Nd. Thus, the rare earth magnet containing Nd has extremely excellent magnetic properties.

  The formation of such a polymer protective layer by electron beam irradiation can be specifically carried out as follows. That is, when the electron beam is irradiated to a partial area on the surface of the magnet body, the polymer protective layer is formed by gradually changing the irradiation area of the electron beam on the surface of the magnet body. Can do.

  In this way, when the irradiated electron beam can irradiate only a partial area of the magnet body, the electron beam is moved in the irradiation area so as to scan the surface of the magnet body. However, the region where the protective layer on the surface of the magnet body is to be formed is irradiated. By doing so, it is possible to selectively form a polymer protective layer in a desired region on the surface of the magnet body.

  In addition, the electron beam applied to the magnet body may be a slit having a short side and a long side. In particular, it is preferable that the long side is larger than a predetermined width direction in the magnet body. In this case, by moving the slit-shaped electron beam in the direction perpendicular to the long side, it is possible to irradiate a wider area with the electron beam, thereby further facilitating the formation of the protective layer. In addition, when a planar electron beam that extends to the entire surface of the magnet body is used, the electron beam irradiation step can be performed in a shorter time, which is preferable.

  And when forming a protective layer with the method mentioned above, it is preferable to form so that the thickness may be set to 0.1-5 micrometers. Since the rare earth magnet of the present invention is formed with a polymer protective layer with few defects, it is not necessary to make the surface protective film thicker than necessary. The rare earth magnet having the protective layer having such a thickness has almost no damage inside the magnet body and has good durability and magnetic properties.

  According to the method for producing a rare earth magnet of the present invention, since a polymer protective layer with few defects can be formed at a low temperature, a protective film having excellent durability and being free from the influence of stress can be obtained. Therefore, it is possible to provide a highly durable rare earth magnet having good magnetic properties.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same element and the overlapping description is abbreviate | omitted.

  First, a rare earth magnet obtained by a manufacturing method according to a preferred embodiment will be described with reference to FIGS.

  FIG. 1 is a perspective view schematically showing a rare earth magnet obtained by the manufacturing method according to the embodiment, and FIG. 2 is a schematic sectional view taken along line II-II of the rare earth magnet 1 shown in FIG. FIG.

  The rare earth magnet 1 includes a magnet body 2 and a protective layer 4 formed on the surface region of the magnet body 2 and has a substantially rectangular parallelepiped structure. The magnet body 2 contains a rare earth element. Here, the rare earth element means an element belonging to the third period of the long-period periodic table and an element belonging to the lanthanoid. Examples of such a rare earth element include yttrium (Y), lanthanum (La), and cerium ( Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium ( Tm), ytterbium (Yb), lutetium (Lu) and the like.

  As the magnet body 2 containing these rare earth elements, those having a composition containing a combination of the rare earth elements and the transition elements are preferable. The magnet body 2 having such a combination preferably contains at least one element selected from the group consisting of Nd, Dy, Pr, and Tb as a rare earth element. These elements include La, Sm, Ce, What further contains at least one element selected from the group consisting of Gd, Er, Eu, Tm, Yb and Y is more preferable.

  More specifically, examples of the constituent material of the magnet body 2 include those having an R—Fe—B (R is a rare earth element) type or R—Co type structure. In the material having the former structure, R is preferably Nd, and in the material having the latter structure, R is preferably Sm.

  Especially, as a constituent material of the magnet body 2 in the rare earth magnet 1, a material having an R—Fe—B structure is preferable. Such a material has a main phase having a substantially tetragonal crystal structure, and a rare earth-rich phase having a high rare earth element content in the grain boundary portion of the main phase, and a boron atom content ratio. Has a high boron-rich phase. These rare earth-rich phase and boron-rich phase are nonmagnetic phases that do not have magnetism, and such a nonmagnetic phase is usually contained in an amount of 0.5 to 50% by volume in the magnet constituting material. Moreover, the particle size of the main phase is usually about 1 to 100 μm.

  In the magnet body 2 having the R-Fe-B-based configuration, the rare earth element content is preferably 8 to 40 atomic%. When the rare earth element content is less than 8 atomic%, the crystal structure of the main phase becomes almost the same as that of α-iron, and the coercive force (iHc) tends to decrease. On the other hand, if it exceeds 40 atomic%, a rare earth-rich phase is excessively formed, and the residual magnetic flux density (Br) tends to be small.

  The Fe content is preferably 42 to 90 atomic%. When the Fe content is less than 42 atomic%, Br decreases, and when it exceeds 90 atomic%, iHc tends to decrease. Furthermore, the B content is preferably 2 to 28 atomic%. When the content of B is less than 2 atomic%, a rhombohedral structure is likely to be formed, and this tends to reduce iHc, and when it exceeds 28 atomic%, a boron-rich phase is excessively formed. Br tends to be small.

  In the constituent materials described above, a part of Fe in R—Fe—B may be substituted with Co. Thus, if a part of Fe is replaced by Co, the temperature characteristics can be improved without deteriorating the magnetic characteristics. In this case, it is desirable that the amount of substitution of Co not be larger than the content of Fe. When the Co content exceeds the Fe content, the magnetic properties of the magnet body 2 tend to be reduced.

  In addition, a part of B in the constituent material may be substituted with an element such as C, P, S, or Cu. By replacing a part of B in this way, the magnet body can be easily manufactured and the manufacturing cost can be reduced. At this time, the substitution amount of these elements is desirably an amount that does not substantially affect the magnetic properties, and is preferably 4 atomic% or less with respect to the total amount of constituent atoms.

  Further, from the viewpoint of improving iHc and reducing manufacturing costs, in addition to the above-described structure, Al, Ti, V, Cr, Mn, Bi, Nb, Ta, Mo, W, Sb, Ge, Sn, Zr, Ni , Si, Ga, Cu, Hf and other elements may be added. These addition amounts are also preferably in a range that does not affect the magnetic properties, and are preferably 10 atomic% or less with respect to the total amount of constituent atoms. In addition, O, N, C, Ca, etc. are conceivable as components inevitably mixed, and these may be contained in an amount of about 3 atomic% or less with respect to the total amount of constituent atoms.

  The protective layer 4 is formed on the surface of the magnet body 2 having the above-described configuration. The protective layer 4 is formed by depositing the above-described monomer / oligomer on the surface of the magnet body 2, or after applying a solution in which the monomer / oligomer is dispersed on the surface of the magnet body 2, and then applying an electron beam on the surface. Is formed by polymerizing the monomer in the solution. That is, the protective layer 4 is configured to include a polymer film polymerized by an electron beam.

  Here, with reference to FIG. 3, the structure of the rare earth magnet 1 in the vicinity of the interface between the magnet body 2 and the protective layer 4 will be described. FIG. 3 is a diagram schematically showing a cross-sectional structure near the interface between the magnet body 2 and the protective layer 4 in the rare earth magnet 1.

  As shown in FIG. 3, the magnet body 2 includes a main phase 22, a boron rich phase 24, and a rare earth rich phase 26 formed therebetween.

  Further, the protective layer 4 made of a polymer formed on the surface of the magnet body 2 is in a state of being formed with a substantially constant thickness from the surface of the rare earth magnet 1. As thickness of this protective layer 4, 0.1-5 micrometers is preferable, 0.5-3 micrometers is more preferable, 1-2 micrometers is still more preferable.

  Thus, in the rare earth magnet 1 formed by the manufacturing method according to the preferred embodiment, the protective layer 4 is selectively formed only in a certain depth region from the surface of the magnet body 2. In general, it is considered that the magnetic properties of rare earth magnets are greatly dependent on the rare earth rich phase present at the grain boundaries of the magnet body. Therefore, since the rare earth magnet 1 configured as described above does not require high-temperature overheating for forming the protective film, the rare earth-rich phase 26 inside the magnet body 2 is in a good state. Therefore, extremely good magnetic properties can be exhibited as compared with a conventional protective film formed by thermal oxidation.

  Next, the suitable manufacturing method of the rare earth magnet 1 which has such a structure is demonstrated. The rare earth magnet 1 can be obtained by manufacturing the magnet body 2 and then forming the protective layer 4 on the surface region of the magnet body 2. Hereinafter, the specific method will be described in detail.

  The magnet body 2 can be manufactured, for example, by powder metallurgy. In this method, first, an alloy (ingot) having a desired composition is manufactured by a known alloy manufacturing process such as a casting method or a strip casting method. Next, this alloy was pulverized to a particle size of 10 to 100 μm using a coarse pulverizer such as a jaw crusher, a brown mill, a stamp mill, and then further reduced to 0 by a fine pulverizer such as a jet mill or an attritor. The particle size should be 5 to 5 μm.

The powder thus obtained is preferably molded by applying pressure in a magnetic field. In this case, the magnetic field strength in the magnetic field is preferably 10 kOe or more, and the molding pressure is preferably about 1 to 5 ton / cm ² . Thereafter, the obtained molded body is preferably quenched in an inert gas atmosphere or under vacuum at 1000 to 1200 ° C. for 0.5 to 10 hours. Further, the sintered body is subjected to heat treatment at 500 to 900 ° C. for 1 to 5 hours in an inert gas atmosphere or vacuum, and then the sintered body is processed into a desired shape to obtain the magnet body 2. .

  In addition to the above-described method, the magnet body 2 can also be manufactured by, for example, a well-known super rapid cooling method, a warm brittle processing method, a casting method, or a mechanical alloying method. Further, as the magnet body 2, a commercially available one may be prepared.

  Next, an organic layer containing an organic starting material is formed on the surface of the magnet body 2 thus obtained.

  The organic starting material can be evaporated inside the vacuum chamber and deposited on the surface of the magnet body 2. As a vapor deposition method, either resistance thermal vapor deposition or electron beam vapor deposition may be used. Thereby, an organic layer having a uniform film thickness can be formed on the surface of the magnet body 2.

  The organic starting material can be applied and deposited on the surface of the magnet body 2 in a solution state. In the solution state, a solvent can be used as appropriate. For example, in the case of an epoxy acrylate that is an oligomer, it exists as a liquid at room temperature, and thus can be applied as it is.

  FIG. 5 is a diagram schematically illustrating a first method for irradiating the magnet body 2 with an electron beam. In this method, an electron beam 40 is irradiated in a spot shape from a portion of one surface of the magnet body 2 from the electron beam irradiation unit 30 in a vacuum apparatus (not shown) whose inside is maintained in an oxidizing atmosphere. . Thereafter, a predetermined electric field is applied to the electron beam 40 by the coil 50 to scan the surface of the magnet body 2, and the irradiation region of the electron beam 40 on the magnet body 2 is gradually changed. Finally, the electron beam 40 is irradiated to all the one surface of the magnet body 2. By irradiating such an electron beam 40 on each surface of the magnet body 2 in the same manner, it is possible to irradiate the entire surface of the magnet body 2 with the electron beam 40. The irradiation region of the electron beam 40 may be changed by gradually moving either the electron beam irradiation unit 30 or the magnet body 2 in addition to the method using the coil 50 described above.

  The electron beam irradiation unit 30 is not particularly limited as long as it is an apparatus that can irradiate the electron beam 40, and emits the electron beam 40 to a known electron gun including an electron emission source, an anode, a cathode for accelerating electrons, and the like. A combination of various external magnetic field application mechanisms for adjustment can be applied. As the electron emission source, a thermoelectron emission source that emits thermoelectrons by heating a filament or the like, or an electron emission source that emits electrons by discharge or the like can be used. The electron beam irradiation unit 30 may include a single thermionic emission source or electron emission source, or a plurality of electron emission sources. As described above, when a plurality of thermionic emission sources and a plurality of electron emission sources are provided, the electron beam can be irradiated over a relatively wide range.

  In the electron beam irradiation unit 30, electrons may be accelerated by an external magnetic field application mechanism together with the anode, the cathode, or the like, or instead of the anode, the cathode, or the like. As this external magnetic field applying mechanism, a known means such as a permanent magnet or a coil can be appropriately selected and used. Examples of such an electron beam irradiation unit 30 include an electron gun used in an electron microscope, a hot cathode electron beam source used in a vapor deposition apparatus, and a hollow cathode discharge electron beam used in a vapor deposition apparatus. The source can be suitably used.

The atmosphere is an atmosphere in which only the polymerization reaction can proceed while suppressing the oxidation reaction occurring in the organic starting material as much as possible in an inert gas atmosphere or in a vacuum. The inert gas atmosphere is preferably N ₂ gas, Ar gas, or the like, for example. As the vacuum condition, the initial pressure inside the electron beam irradiation apparatus is set to about 10 ⁻⁶ to 10 ⁻⁴ Pa, and then the electron beam irradiation is performed at the same pressure as the initial pressure, or the above inert gas is introduced. it is preferable to perform to a partial pressure as ¹⁰ -3 ^~10 0 Pa. The inert gas atmosphere is more preferably 5 × 10 ⁻² to 10 ⁻¹ Pa, further preferably 1 × 10 ^{−1 to} 5 × 10 ⁻² Pa. When the electron beam 40 is irradiated under such conditions, the organic layer is polymerized well, thereby facilitating the formation of the protective film 4.

  The irradiation time of the spot-like electron beam 40 is preferably about 0.5 to 600 seconds, more preferably about 1 to 400 seconds, and still more preferably 5 to 200 seconds with respect to the region that can be irradiated at once. To the extent. When the irradiation time is less than 0.5 seconds, the polymerization reaction of the organic starting material by the electron beam 40 becomes insufficient, and the protective layer 4 tends not to be sufficiently formed. On the other hand, if it exceeds 600 seconds, local reradicalization and polymer dissociation may occur.

  FIG. 6 is a diagram schematically illustrating a second method for irradiating the magnet body 2 with the electron beam 40. As shown in the figure, the electron beam irradiation unit 32 can irradiate the magnet body 2 with an electron beam 40 so as to form a rectangular slit-shaped irradiation region. Examples of the electron beam irradiation unit 32 include those configured to emit a slit-shaped electron beam, and those arranged in parallel with a plurality of electron beam irradiation units that emit electron beams in a spot shape as described above. Can be used.

  A predetermined electric field is applied to such an electron beam 40 by the coil 52, and the irradiation region of the slit-like electron beam 40 in the magnet body 2 is gradually changed in a direction perpendicular to the long side. In this case, as compared with the electron beam 40 serving as the spot-shaped irradiation region described above, a wide region can be irradiated by one scanning. In particular, as shown in the drawing, it is preferable that the long side of the electron beam 40 irradiated in a slit shape is the same as or longer than a predetermined one side in the magnet body 2. By so doing, the electron beam 40 can be irradiated so as to cover the entire surface of the magnet body 2 by moving the slit-shaped irradiation region in one direction.

  Then, the irradiation of the slit-shaped electron beam 40 is similarly performed on each surface of the magnet body 2. As a result, the polymerization reaction of the organic layer proceeds in the region irradiated with the electron beam 40, and the protective layer 4 made of a dense polymer material is formed on the surface of the magnet body 2. In addition, the other conditions at the time of electron beam 40 irradiation are the same as the suitable conditions in a 1st method.

  In this way, the protective layer 4 made of a dense polymer material can be formed in the vicinity of the surface of the magnet body 2 by the first method and the second method. For example, in the first method, since the electron beam 40 can be irradiated in a spot shape, the electron beam 40 can be irradiated only on a predetermined region on the surface of the magnet body 2. Therefore, according to the first method, it is easy to selectively form the protective layer 4 in a desired region on the surface of the magnet body 2. In the second method, since the electron beam 40 can be irradiated in a slit shape, the electron beam 40 can be irradiated over a wide range by moving in one direction. For this reason, for example, when forming the protective layer 4 in the whole surface of the magnet element | base_body 2, the advantage that an operation | work can be completed in a short time is acquired.

  In this way, by irradiating the magnet body 2 with the electron beam, the rare earth magnet 1 having the protective layer 4 formed on the surface of the magnet body 2 is obtained. The rare earth magnet 1 thus manufactured has the following characteristics.

  That is, the rare earth magnet 1 has a protective layer 4 made of a dense polymer material in which an organic layer formed on the magnet body 2 is polymerized by irradiating the magnet body 2 with an electron beam. According to the electron beam irradiation, a selective polymerization reaction can be caused only in the region near the surface of the magnet body 2 in a short time, and therefore the protective layer 4 has a uniform thickness on the surface of the magnet body 2. Will be formed. Such a rare earth magnet 1 has an inner portion of the magnet body 2 in comparison with a conventional polymer film in which a protective layer is formed by long-time and high-temperature heating, and in comparison with a polymer film in which a polymerization initiator remains. Damage is extremely low. For this reason, even after the protective layer 4 is formed, sufficiently excellent magnetic properties are maintained.

  Further, since the protective layer 4 is formed by low temperature polymerization, that is, without thermal expansion as described above, the adhesion to the magnet body 2 is extremely high without suffering from the influence of stress. Therefore, when the protective layer 4 is formed, the layer is hardly peeled to form particles, and stress is hardly generated in the layer. Therefore, the protective layer 4 formed in this way has extremely few occurrences of pinholes, peeling and the like as compared with the conventional case.

  As described above, the rare earth magnet 1 obtained by the manufacturing method of the present embodiment sufficiently maintains the excellent magnetic properties that the magnet element body 2 originally has. In addition, since the protective layer 4 has very few defects, it has excellent durability. Therefore, for example, it can be suitably used in fields that require excellent magnetic properties and durability, such as fuel cell vehicles and drive motors for hybrid cars.

  As mentioned above, although the embodiment of the suitable manufacturing method of the rare earth magnet of this invention was described, this invention is not limited to the said embodiment, A various deformation | transformation is possible in the range which does not deviate from the summary. For example, the rare earth magnet 1 may further include a metal oxide layer, a metal layer, or the like for improving durability on the surface of the protective layer 4.

  Further, the electron beam irradiation process is not necessarily performed under reduced pressure in the vacuum apparatus as described above, and can be performed under atmospheric pressure or a pressure near atmospheric pressure as long as a good inert gas atmosphere can be maintained. You can also

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples.

[Example]
(Manufacture of rare earth magnets)
A sintered body having a composition of 14Nd-1Dy-7B-78Fe (numbers are atomic ratio) prepared by powder metallurgy is heat-treated at 600 ° C. for 2 hours in an argon gas atmosphere, and then 56 × 40 × 8 (mm ) In the shape of a rectangular parallelepiped, and further chamfered by barrel polishing to obtain a magnet body. Next, this magnet body was washed with an alkaline degreasing solution, then the surface was activated with a nitric acid solution, and then sufficiently washed with water.

The magnet body after washing with water was placed in a predetermined vacuum device together with a tungsten boat on which an acrylate monomer was placed, and the inside of the device was evacuated until the pressure became 1 × 10 ⁻⁴ Pa. Thereafter, the tungsten boat was energized and heated in this vacuum apparatus, and the acrylate monomer was deposited on the magnet surface.

  Thereafter, an electron gun installed in the vacuum device was driven under the conditions of 6 kV and 50 mA, and a predetermined region on one surface of the magnet body was irradiated with a spot-like electron beam. And the electron beam irradiation area | region in this one surface was changed gradually, and the whole surface of the said surface was irradiated with the electron beam. And the same operation | work was performed with respect to each surface of a magnet element | base_body, and thereby the polymer layer of thickness 1.5micrometer was formed in all the surfaces in a magnet element | base_body.

(Characteristic evaluation)
The obtained rare earth magnet was subjected to a humidification high temperature test (PCT test) for 24 hours at 120 ° C. and 0.2 × 10 ⁶ Pa in a steam atmosphere. As a result, no weight reduction of the rare earth magnet after the PCT test was observed. Further, when the rare earth magnet after the PCT test was visually observed, it was confirmed that the protective layer had no defects such as pinholes and cracks.

It is a perspective view which shows typically the rare earth magnet obtained by the manufacturing method which concerns on embodiment. It is a figure which shows typically the cross-sectional structure along the II-II line of the rare earth magnet 1 shown in FIG. 2 is a diagram schematically showing a cross-sectional structure in the vicinity of an interface between a magnet body 2 and a protective layer 4 in a rare earth magnet 1. FIG. It is a figure which shows typically the cross-sectional structure of the interface vicinity of a magnet element body and a protective layer in the rare earth magnet which formed the protective layer by the conventional thermal oxidation etc. It is a figure which illustrates typically the 1st method for irradiating the electron beam 40 to the magnet body. It is a figure which illustrates typically the 2nd method for irradiating the electron beam 40 to the magnet body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Rare earth magnet, 2 ... Magnet body, 4 ... Protective layer, 22 ... Main phase, 24 ... Boron rich phase, 26 ... Grain boundary, 30, 32 ... Electron beam irradiation part, 40 ... Electron beam, 50, 52 ... coil.

Claims (10)

To magnet body containing rare earth elements,
After depositing an organic layer containing organic starting materials,
A method for producing a rare earth magnet, comprising irradiating an electron beam to a magnet body provided with the organic layer.   The method for producing a rare earth magnet according to claim 1, wherein the organic starting material is a crosslinked monomer.   The method for producing a rare earth magnet according to claim 1, wherein Nd is contained as the rare earth element.   The rare earth magnet according to any one of claims 1 to 3, further comprising a polymerization reaction step of polymerizing the organic layer to form the protective layer by irradiating the electron beam. Production method.   The method for producing a rare earth magnet according to any one of claims 1 to 4, wherein an irradiation region of the electron beam on the surface of the magnet body is changed.   The method of manufacturing a rare earth magnet according to claim 1, wherein the electron beam is irradiated in a rectangular slit shape. The electron beam irradiation step includes
The method for producing a rare earth magnet according to any one of claims 1 to 6, wherein the method is performed in an inert gas atmosphere or in a vacuum.   The method for producing a rare earth magnet according to claim 1, wherein the protective layer is formed to have a thickness of 0.1 to 5 μm. The deposition step includes
The method for producing a rare earth magnet according to any one of claims 1 to 8, further comprising a step of depositing the organic starting material on a surface of the magnet body using an evaporation method. The deposition step includes
The organic starting material,
The method for producing a rare earth magnet according to any one of claims 1 to 9, further comprising a step of dispersing in a solvent and applying to a magnet surface.

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